Thin wafer handling method

CROSS-REFERENCE TO RELATED APPLICATIONS

0001The present application is a continuation-in-part of U.S. patent application Ser. No. 12/818,362 filed on Jun. 18, 2010, which claims priority of U.S. Provisional Patent Application Ser. No. 61/221,890 filed on Jun. 30, 2009, both of which are entirely incorporated by reference herein.

TECHNICAL FIELD

0002This disclosure relates generally to wafer processing and more particularly to a thin wafer handling structure and method to facilitate bonding and debonding.

BACKGROUND

0003In semiconductor wafer processing, temporary bonding and debonding techniques are necessary for thin wafer backside processes. The wafer is bonded on a rigid carrier by adhesive layers. After grinding and/or other post-bonding processes, the wafer is debonded from the rigid carrier.

0004One of the conventional debonding methods uses a laser on a light-to-heat conversion layer (LTHC) to release the carrier, and then peel off the adhesive. The adhesive material is UV-cured material, e.g., thermal setting polymer, that cannot be stripped by chemicals and should be peeled off instead. This method suffers chemical residue after debonding. Also, the laser release layer has a weak chemical resistance during backside processes.

0005Another conventional method uses chemical release. This method chemically dissolves the adhesive to release the wafer from the carrier. This method needs perforated glass and easily induces cross contamination. The process speed, e.g., wafers per hour (WPH), is also slow compared to the other methods.

0006Yet another conventional method is thermal sliding. This method treats the wafer and carrier with heat and then slides them apart. This method needs higher debonding temperatures and may adversely impact the interconnection scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

0007For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

0008<figref idref="DRAWINGS">FIG. 1</figref> illustrates an example of a thin wafer handling structure to facilitate bonding and debonding according to one aspect of the present disclosure;

0009<figref idref="DRAWINGS">FIG. 2</figref> illustrates an example method to facilitate thin wafer bonding and debonding according to another aspect of the present disclosure;

0010<figref idref="DRAWINGS">FIG. 3</figref> illustrates another exemplary embodiment of the thin wafer handling structure according to one aspect of the present disclosure; and

0011<figref idref="DRAWINGS">FIG. 4</figref> illustrates another exemplary method to facilitate thin wafer bonding and debonding according to another aspect of the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

0012The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosure, and do not limit the scope of the invention.

0013A thin wafer handling structure and method to facilitate bonding and debonding for wafer process are provided. Throughout the various views and illustrative embodiments of the present disclosure, like reference numbers are used to designate like elements.

0014<figref idref="DRAWINGS">FIG. 1</figref> illustrates an example of a thin wafer handling structure to facilitate bonding and debonding according to one aspect of the present disclosure. The wafer <b>102</b> is bonded on the carrier <b>108</b> using two layers in between, i.e. the release layer <b>106</b> and the adhesive layer <b>104</b>. The release layer <b>106</b> is applied on carrier <b>108</b> by coating or lamination processes followed by removal of the outer most 0.1 mm-3 mm of the release layer <b>106</b> from the edge of the carrier by edge bead removal (EBR). EBR removes a build-up of material at the wafer edges. Without any intervention, excess material may accumulate at the edge of the wafer at up to several times the nominal thickness of the layer. Such a condition would present a significant contamination risk for process equipment. For chemical EBR, solvent is dispensed on the edge of the wafer as the wafer is rotated immediately after coating.

0015The release layer <b>106</b> can comprise light-to-heat conversion (LTHC) layer such as epoxy or acryl-based polymer. The carrier <b>108</b> can be released by energy application on the release layer <b>106</b>, e.g., ultraviolet (UV) or near infra-red (NIR) laser, or thermal treatment.

0016The adhesive layer <b>104</b> is applied on wafer <b>102</b> by coating or lamination process, and should be capable of being removed by solvent, e.g., thermal plastic polymer can be used as the adhesive layer <b>104</b> in one preferred embodiment. The carrier <b>108</b> and the wafer <b>102</b> are bonded together by UV light or thermal energy.

0017Thermal plastic polymer (also referred to as thermoplastic material) includes polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), adipic ester (ADP), or any combination thereof, and other long-chain materials.

0018Even though an adhesive layer and release layer combination <b>103</b> in <figref idref="DRAWINGS">FIG. 1</figref> shows one adhesive layer <b>104</b> with the release layer <b>106</b> to help temporary bonding of the wafer <b>102</b> and the carrier <b>108</b>, the adhesive layer <b>104</b> can comprise multiple adhesive layers in some embodiments as shown in <figref idref="DRAWINGS">FIG. 3</figref>.

0019<figref idref="DRAWINGS">FIG. 2</figref> illustrates an example method to facilitate thin wafer bonding and debonding according to another aspect of the present disclosure. At step <b>202</b>, the release layer <b>106</b> is applied on the carrier <b>108</b> by coating or lamination. Spin coating can be used for release layer application according to one embodiment. At step <b>204</b>, the adhesive layer <b>104</b> is applied on the wafer <b>102</b> by coating or lamination. At step <b>206</b>, the carrier <b>108</b> and the wafer <b>102</b> are bonded together with the release layer <b>106</b> and the adhesive layer <b>104</b> in between and cured by thermal energy or UV light. The adhesive can be pre-baked prior to bonding. At step <b>208</b>, the wafer goes through post-bonding processes, e.g., grinding, wafer backside processing, etc. The wafer backside processing may include ion implantation, annealing, etching, sputtering, evaporation, and/or metallization, etc.

0020After the post-bonding processes, the wafer goes through the debonding processes, which includes carrier release and post cleaning. At step <b>210</b>, the carrier <b>108</b> is released by energy application on the release layer <b>106</b>, e.g., UV or NIR light from a laser, or thermal treatment. The thin wafer <b>102</b> can be attached on dicing frame for dicing tape lamination prior to releasing the carrier. Then the wafer <b>102</b> surface is cleaned by chemical soaking in solvent to remove any residue of the adhesive layer <b>104</b>. For example, an adhesive layer <b>104</b> using thermal plastic polymer can be chemically cleaned with a solvent. A skilled person in the art will appreciate that there can be many embodiment variations of this disclosure.

0021In some embodiments, an organic type solvent can be used as the solvent to clean and remove the adhesive layer <b>104</b>. In other embodiments, different methods such as ashing or surface grinding process can be used to remove the adhesive layer <b>104</b>. In one example, an ashing process using strongly oxidizing ambient, such as oxygen plasma ashing, can be used. In another example, any suitable surface grinding method including chemical mechanical polishing (CMP) can be used. Ashing can provide relatively uniform surface removal, and surface grinding can provide a cost-effective way of removal.

0022<figref idref="DRAWINGS">FIG. 3</figref> illustrates another exemplary embodiment of the thin wafer handling structure according to one aspect of the present disclosure. There are two adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>shown in <figref idref="DRAWINGS">FIG. 3</figref>. The adhesive layer <b>104</b><i>a </i>adjacent to a wafer <b>102</b> comprises thermoplastic material or thermoset material and the adhesive layer <b>104</b><i>b </i>adjacent to the release layer <b>106</b> can comprise thermoset material or thermoplastic material in some embodiments.

0023Thermoset material for the adhesive layer <b>104</b><i>b </i>can be curable short-chain polymer materials, such as UV epoxy, Benzocyclobutene (BCB), Methylsilsesquioxane (MSQ), polyimides, and other short-chain polymers. Thermoplastic material for the adhesive layer <b>104</b><i>a </i>can comprise polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), Adipic ester (ADP), any combination thereof, or other long-chain materials.

0024The thickness of the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>can vary depending on the wafer size and the surface structure of the wafer <b>102</b>. For example, with a wafer size of about 30 cm (or surface with up to 120 μm height variation), the total thickness of adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>can range from 10 μm to 250 μm, the thickness of the adhesive layer <b>104</b><i>a </i>can range from 0.5 μm to 50 μm, and the thickness of the adhesive layer <b>104</b><i>b </i>can range from 9.5 μm to 200 μm.

0025The multiple adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>helps to protect device surface of the wafer <b>102</b>, and also provides better process compatibility such as better temperature/pressure property. For example, for metallization in a redistribution layer (RDL) process, a high temperature up to 350° C. or more can be reached. When the adhesive layer <b>104</b><i>b </i>comprises thermoset material with better high temperature property, and the adhesive layer <b>104</b><i>a </i>comprises thermoplastic material with better cleaning property, such adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>are suited for the RDL process, compared to one adhesive layer comprising thermoplastic material. Such adhesive layer structure using multiple adhesive layers reduces wafer cracks and residue after debonding, helps to maintain a robust line yield during post bonding processes, and saves the cost of bond/debond process for high volume production.

0026In some embodiments, different material combinations of the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>can be selected based on temperature property, structure protection, and/or cleaning, among other properties. In some embodiments, the adhesive layer <b>104</b><i>a </i>can be selected based on the protection property of the wafer <b>102</b>. For example, the adhesive layer <b>104</b><i>a </i>can comprise polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), or adipic ester (ADP), and the adhesive layer <b>104</b><i>b </i>can comprise PE or PP for the adhesive property.

0027In some embodiments when thermoplastic materials are used for adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b</i>, different materials such as PP, PE, PET, polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), adipic ester (ADP), or any combination thereof, can be used for adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b</i>. In some other embodiments, the same thermoplastic material can be used for both adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b</i>. In some embodiments, more than two adhesive layers can be used, such as three, four, etc.

0028The release layer <b>106</b> can comprise a light-to-heat conversion (LTHC) layer such as epoxy or acryl-based polymer. The carrier <b>108</b> can be released by energy application on the release layer <b>106</b>, e.g., UV or NIR laser, or thermal treatment.

0029<figref idref="DRAWINGS">FIG. 4</figref> illustrates another exemplary method to facilitate thin wafer bonding and debonding according to another aspect of the present disclosure. At step <b>402</b>, the release layer <b>106</b> is formed on the carrier <b>108</b> by coating or lamination, for example. At step <b>404</b>, one adhesive layer such as <b>104</b><i>a </i>is formed on the wafer <b>102</b> by coating or lamination, for example. Spin coating can be used for release layer <b>106</b> and adhesive layer <b>104</b><i>a </i>according to some embodiments.

0030At step <b>406</b>, at least one additional adhesive layer such as <b>104</b><i>b </i>is formed over the release layer <b>108</b> or the previously formed adhesive layer <b>104</b><i>a </i>by coating or lamination (before bonding the carrier <b>108</b> with the wafer <b>102</b>). If the additional adhesive layer such as <b>104</b><i>b </i>is formed over the previously formed adhesive layer <b>104</b><i>a</i>, the adhesive layer <b>104</b><i>a </i>can be cured by thermal treatment prior to forming the additional adhesive layer <b>104</b><i>b</i>. For example, a thermal treatment with the temperature ranging from 150° C. to 350° C. can be used for less than 2 hours in some embodiments.

0031At step <b>408</b>, the carrier <b>108</b> and the wafer <b>102</b> are bonded together with the release layer <b>106</b> and the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>in between and cured by thermal energy or light from UV or NIR laser. For example, light from a UV laser with a wavelength in the range from 250 nm to 400 nm, or an NIR laser with a wavelength in the range from 1000 nm to 1300 nm can be used in some embodiments. For thermal energy, a temperature ranging from 150° C. to 350° C. can be used for less than 30 minutes in some embodiments. The adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>can be pre-baked prior to bonding in some embodiments.

0032At step <b>410</b>, the wafer <b>102</b> goes through post-bonding processes, e.g., grinding, wafer backside processing, wafer metal routing (such as RDL), etc. The wafer backside processing may include ion implantation, annealing, etching, sputtering, evaporation, and/or metallization, among other processes.

0033After the post-bonding processes, the wafer goes through the debonding processes, which includes carrier release and post cleaning. At step <b>412</b>, the carrier <b>108</b> is released by energy application on the release layer <b>106</b>, e.g., UV or NIR laser, or thermal treatment. The thin wafer <b>102</b> can be attached on dicing frame for dicing tape lamination prior to releasing the carrier.

0034At step <b>414</b>, the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>are removed. Ashing, cleaning, surface grinding, or any combination thereof can be used to remove the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b </i>after debonding the wafer <b>102</b> from the carrier <b>108</b>. Ashing can provide relatively uniform surface removal, and surface grinding can provide a cost-effective way of removal. For cleaning, the wafer <b>102</b> surface can be cleaned by chemical soaking in solvent such as organic type solvent to remove any residue of the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b</i>. In some embodiments, one step cleaning can be used to remove the adhesive layers <b>104</b><i>a </i>and <b>104</b><i>b</i>. In other embodiments, multiple steps can be used such as grinding and then cleaning, ashing and then cleaning, or two cleaning steps.

0035The wafer handling method using multiple adhesive layers as described above reduces wafer cracks and residue after debonding, helps to maintain a robust line yield during post bonding processes, and saves cost of bond/debond process for high volume production.

0036According to some embodiments, a method includes receiving a carrier with a release layer formed thereon. A first adhesive layer is formed on a wafer. A second adhesive layer is formed over the first adhesive layer or over the release layer. The carrier and the wafer are bonded with the release layer, the first adhesive layer, and the second adhesive layer in between the carrier and the wafer.

0037According to some embodiments, a method includes receiving a carrier bonded to a wafer. A release layer and two adhesive layers are formed between the carrier and the wafer. The carrier is released by applying ultraviolet (UV) light, near infrared (NIR) laser, or thermal energy.

0038According to some embodiments, a method includes forming a first adhesive layer comprising thermoplastic material on a wafer. A second adhesive layer comprising thermoset material is formed on the first adhesive layer. At least one of the first adhesive layer or the second adhesive layer is cured. The wafer is bonded to a carrier. The carrier is released by applying energy. The first adhesive layer and the second adhesive layer are removed by cleaning.

0039The advantageous features of the present disclosure include surface cleanness after debonding and good chemical resistance during post-bonding processes. Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure.